Substrates are commonly exposed to liquids during semiconductor processing. For example, a substrate may be chemically etched and cleaned many times during the course of fabrication. Typically, a water rinse follows each etch and cleaning operation. It is important that any liquid is removed, preferably completely, from the substrate to avoid defects in the finished product.
Many of the semiconductor processing operations that involve liquids are performed in a batch mode. However, many other processing operations are performed in a single substrate mode. For example, the processing operations of dry etching and deposition are typically performed on an individual substrate. Because of the variable delay between the cleaning process and other processes caused by having both batch and single substrate modes of processing, it would be desirable to have a single mode of processing a substrate.
One of the difficulties in converting the wet processing operations from a batch mode to a single substrate mode is the inability to remove liquids completely from the surface of a substrate during single substrate processing. One of the reasons for this difficulty is that in a single substrate mode the substrate is generally positioned horizontally. The difficulty arises because the liquids need to be removed from both the top and bottom surfaces of the substrate when positioned horizontally.
One common method of removing liquids from a substrate surface is based on the Marangoni principle. The Marangoni principle provides that when substrates are pulled slowly through a water surface and a surface tension lowering substance is added, the surface tension gradient draws the water away from the surface, leaving it dry. However, liquid removal techniques that rely on the Marangoni principle require the substrates to be located in a vertical position.
Spin drying methods allow for horizontal substrate positioning. Spin dryers use high-speed rotation to literally throw the liquid off of the substrate surface. However, this technique leaves undesirable residues, commonly referred to as drying marks, on the substrate surface. These drying marks are undesirable as they can cause defects in the finished product.
A further limitation associated with removing liquids from a substrate surface in a single substrate operation mode is the desire to be efficient. Current semiconductor production lines process a substrate approximately every 1 to 3 minutes. Ideally, a liquid removal operation should also be completed in this amount of time.
Drying methods that use surface tension reducing vapor do not efficiently remove liquid from a horizontally positioned substrate. In this regard, because the surface tension reducing vapor is passively applied, it is difficult to control the vapor and to efficiently remove the liquids. Additionally, such methods may not be suitable for removing liquids simultaneously from both the top and the bottom of a substrate that is horizontally positioned.
Therefore, it would be desirable to have a system and method of efficiently removing liquid from a surface of a substrate positioned horizontally in a single substrate processing mode.